The Cell Biology/Morphology Core facility in the Renal Unit of the Massachusetts General Hospital provides intellectual and technical support for a large number of NIH-funded investigators both within the MGH community, and in other local and national institutions. Laser confocal microscopy is a major technique that is available to this user base via this Core facility. The confocal microscope currently in use is a BioRad MRC 600 that was purchased 8 years ago. Recent advances in both hardware and software have made this MRC600 unit obsolete. In order for the Core to maintain a state-of-the-art presence in this field of microscopy, an upgrade to the most recent model, a BioRad MRC1024, is urgently required. The purpose of this application is to request funds for such an upgrade from a BioRad MRC600 to an MRC1024 confocal microscope. With the existing system, the sophisticated imaging features that are common in newer microscopes cannot be offered. In addition, the newer systems are simply superior in all aspects of the technique, including basic resolution, sensitivity, and multiple- wavelength separation and 2-D and 3-D imaging and rendering. The Core facility supports projects with a wide-variety of goals, ranging from examining epithelial cell polarity in kidney, reproductive tract, and the GI tract, to studying angiogenesis in tumors in situ. Confocal microscopy is used to perform localization studies on a variety of membrane-associated and intracellular antigens in cells and tissues, as well as to perform fluorescent tracer uptake studies, and to follow the expression of chimeric proteins coupled to green-fluorescent protein (GFP) and expressed in cultured cells. Among the NIH grants supported by the Core are an NIH Program Project (DK38452 - PI: Dennis Brown), a Center for the Study of Inflammatory Bowel Diseases (DK43351 - PI: Dr. D. Podolsky), and numerous individual RO1 grants. In addition, the Core is a central resource in a pending O'Brien Kidney Center application (PI: Dr. M. Hediger, Brigham and Women's Hospital) and an NIH GI Program Project renewal application (PI: Dr. A. Walker, MGH Pediatric GI Unit). The wide-range of biological problems covered by the individual projects that form this proposal, their dependence on the latest techniques in confocal microscopy, demonstrates the great need for upgrading the existing confocal Core facility in order to obtain maximum benefit from the large NIH investment in these multiple projects.